In view of the unique composition of hair fibers and the various changes in style and fashion, the permanent waving of hair has long been of particular interest. In order to best understand the various methods by which hair fibers can be styled or waved, it is important to remember that hair fiber is a proteinaceous material which has many chemical characteristics that relate to manageability, body, texture, static behavior, combability, and sheen. These characteristics may be altered with treatments of surface active agents, salts and polymers such as polysiloxanes, polyoxyalkylenes and polyvinyl pyrrolidones by altering the chemical structure of hair keratin.
It is well known that the three dimensional structure of hair keratin and its stability is related to hydrogen, coulombic, Van der Waals, and disulfide (S--S) bonds which link adjacent protein chains. These forces have also been described as comprising three major bonds that hold the configuration of the hair and are responsible for the strength of the hair. These three bonds are salt linkages, hydrogen bonds, and disulfide bonds. In dealing with these bonds, the hydrogen, coulombic, and Van der Waals forces are weak interactions and are highly dependent upon the water content in the hair keratin. Therefore, only temporary results are obtained by altering these weak interactions.
Because they are so numerous, the hydrogen bonds, involving the amino hydrogen and carbonyl oxygen of the amide linkages, are most important. Water, particularly in the monomolecular state, as occurs with moisture in the air (humidity), can weaken these bonds, by becoming a part of a hydrogen bonding structure. However, some of these hydrogen bonds are protected by hydrophobic bonds and will remain even when the hair is wet with water. More powerful hydrogen bond breakers, like high concentration of lithium bromide and urea are required for complete breakage of all hydrogen bonds.
As long as the hair fiber is dry, the strength of the hair fiber is not reduced. For example, a straight hair, wet with water and held by mechanical force in a curly configuration while drying will remain in a curly shape due to the formed hydrogen bonds and salt linkages, and it will not return to its straight shape so long as it remains dry. However, unless mechanically restrained, upon being wet with water, the hair will lose its curly configuration and become straight.
Normal or virgin hair is usually hydrophobic and many of the chemical treatments remove the natural hydrophobic components of hair. This decrease in hydrophobicity causes an increase in hair porosity resulting in increased rate of water absorption. The water-swollen hair is much more susceptible to mechanical stress such as stretching and breaking. Since hair is an elastic structure, the most common problem in hair setting, is the tendency to return to its natural shape. This tendency is highly accelerated under conditions of high humidity. The rate of return of hair into its natural configuration, is dependent on the method of hair deformation used.
Furthermore, when hair is set by the use of water alone, the hair will gradually lose its curly shape through the absorption of atmospheric moisture and the resulting rearrangement of the hydrogen bonds. This is due to the fact that in water, the dominant bonds are disulfide bond, while in the dry state, the dominant bonds are the salt linkages and the hydrogen bonds.
It is well know that hair fibers are composed of a unique protein called "keratin" which is distinguished by the fact that it contains a very significant amount of an amino acid (cystine) which contains the element sulfur in addition to the elements nitrogen, oxygen, carbon and hydrogen. In the natural synthesis of hair, the element sulfur covalently links intra or inter polypeptide chains (K) through two sulfur atoms (S--S) to give keratin protein (K--S--S--K). Only by chemical action can this covalent linkage be broken.
Since these disulfide bonds are much stronger than the bonds detailed above and are not affected by water, permanent results are obtained by altering the disulfide bonds through cleavage and recombination. In this way, a permanent configuration change of the hair is attained. However, chemical action is required in order for this disulfide linkage to be broken. In this regard, many prior art compositions have been developed for the cold permanent waving of hair. Typically, these prior art systems treat the hair with reducing agents which break the disulfide (cystine) linkage in the hair, while the hair is wound around a curling rod.
In general, permanent hair waving is usually carried out by subjecting the hair to reagents containing a free--SH group or thiol. These materials are also called mercaptans. In this treatment, the hair usually is either wrapped on the rods with water or the lotion containing the thiol, and then saturated with thiol lotion. The thiol waving agent acts to break the disulfide bonds within the hair fiber forming thiol groups in the hair protein and disulfide bonds between two thiol waving agent molecules. The chemistry involved in the reaction of the mercaptan with the cystine disulfide bonds in the hair fiber is illustrated by the following chemical equations (i), (ii) and (iii): ##STR1##
When a sufficient number of hair disulfide bonds have been broken, the hair is realigned to pair previously unpaired hair protein thiol groups opposite each other. At this point, the hair is rinsed, removing the unreacted thiol waving agent and any water soluble disulfide reaction product formed from it. Then, the hair is saturated with an oxidizing agent, or neutralizer, such as hydrogen peroxide or bromate salt, to reform disulfide bonds between the newly paired hair protein thiols, thereby giving the hair a new configuration or wave, or adding curl to the hair. By rebonding the sites of the reduced keratin in their new curled configuration, a permanent set which is impervious to water is established.
Much of the rebonding of the reduced sites is accomplished by the action of the chemical oxidizing agent, which is typically hydrogen peroxide, and can be illustrated by the following chemical reaction: EQU 2 KSH+H.sub.2 O.sub.2 .fwdarw.KSSK+2H.sub.2 O
In the art of permanent waving, there is much trial and error, with the hair being over-processed, in some instances. The characteristics of overprocessing are raspy feel to the hair or a bleaching of the natural underlying color. Structural evaluation of the hair fiber by instrumentation usually reveals that the structural integrity of the hair is lessened, which is evidenced by either an increase in the amount of cysteine and cysteic acid or a lessening of the cystine content relative to the hair not so processed.
Some detrimental effect to hair fiber is unavoidable, as the process of permanent waving involves controlled bond scission of the disulfide linkages within the keratin proteins. Recovery of these disulfides is the determining factor for the tightness of the curls and overall tensile strength. Typically, in order to reshape hair fibers into a lasting configuration, 20% to 50% of available disulfide bonds must be cleaved and reformed into the new configuration. If insufficient disulfide bonds are broken, the hair fiber will rapidly regain natural configuration.
In spite of the substantial effort that has occurred in the development of various permanent waving composition of this general nature, there has been a general inability to improve the holding power or curl configuration retention of "cold permanent waving" formulations. The typical problem encountered with the use of mercaptan reducing agents for the permanent waving of hair is that the permanency of the curl will not last until it is cut off. Instead, the curl relaxes slowly from the normal wear and tear of every day hair care. In this normal grooming process of shampooing, combing, drying and brushing the hair, the fibers are constantly being put under tension and exposed to forces that oppose the new disulfide and hydrogen bonds that were created in the new curl configuration.
In addition to longer curl retention, the industry has also sought to increase the luster, sheen, gloss and manageability of the hair, as well as provide a permanently waved head of hair which is soft, supple, and possesses a natural feel. However, these goals have not been fully attained.
Furthermore, permanent change in hair keratin coupled with operator error, provides inevitable damage to the hair fibers. This damage is measured by evaluating the tensile strength of hair keratin fibers caused by these chemical treatments. Therefore, it would be advantageous to provide treatments that would produce results of a permanent nature and minimum damage to hair keratin.
Since physical and chemical change in the keratin structure of hair fibers are observed during the deformation and relaxation of hair, researchers have tried to minimize the rate of hair relaxation caused by natural forces and water, utilizing treatments of naturally occurring or synthetic polymers. Some surface polymer treatments have had temporary effect on promoting cohesion and decreasing or retarding the rate of water uptake by the hair fiber, while other treatments have attained temporary improvement of such physical characteristics as sheen, manageability and strength. However, these prior art conditioning agents merely provide a temporary benefit and are incapable of satisfying the long-felt need for substantially permanent hair condition improvement.
Therefore, it is a principal object of the present invention to provide a composition for permanently waving hair fibers and a method for employing a permanent waving composition which is capable of imparting to the head of hair a durable, long-lasting permanent hair set retention.
Another object of the present invention is to provide a permanent wave composition and method of applying a permanent wave composition having the characteristic features described above which is capable of conditioning the hair fibers and improving physical properties of the treated hair such as shine, luster, softness, manageability, hair body, and thickness.
Another object of the present invention is to provide a permanent wave composition and method for applying a permanent wave composition to a head of hair having the characteristic features described above which is capable of imparting a long-lasting permanent wave or setting property to the hair, while substantially reducing hair damage caused during the reduction and oxidation processes.
A further object of the present invention is to provide a permanent wave composition and a method for applying a permanent wave composition to a head of hair having the characteristic features described above which is capable of improving the elastic and tensile properties of the hair fibers.
Another object of the present invention is to provide a permanent wave composition and a method for applying a permanent wave composition to a head of hair having characteristic features described above which is capable of attaining all of the desirable features while being employed during the actual reduction process or as a post-reduction step.
Other and more specific objects will in part be obvious and will in part appear hereinafter.